Publication: The Mechanics Magazine
THE (AMERICAN) MUNICIPAL FIRE TELEGRAPH.
The signal stations of Boston consist of cut-iron boxes of great strength fastened to the outside of buildings, and connecting with the wires above by means of insulated conductors, enclosed in an iron gas-pipe. Each of these boxes contains a signal key for police communication, and also for some uses of the Fire Department—an electromagnet included in the circuit, and having an armature carrying a hammer, which raps against the side of the box, as a means of retain communication by sound from the central station,—a discharger of atmospheric electricity, which has already been mentioned, and a signal crank, by which the existence and location of a fire is made known to the centre. The signal crank carries a circuit wheel, either on its axis or at a slower rate by means of gearing, which wheel has the proper number of teeth or cams on its periphery to lift a spring and break the circuit in such a manner as to signalize the number of the fire district, and also the number of the station, to the centre, at each revolution. The number of the fire district is given in dots, that of the number of the station by a combination always of dots and lines. Thus the record produced at the central station, by each rotation of the crank in the box, marked district No. 3, station No. 4, might be as follows:
The name of the person keeping the key of each signal box is marked upon the door. In case of fire the box is opened, and the crank turned half a dozen or a dozen times. The locality of the signal boxes is carefully chosen, usually opposite to a gas lamp. The central station in Boston is the City Building, from a bracket on the roof of which the wires radiate in all directions. Here the receiving Instruments connected with the signal circuits, the transmitting instruments connected with the alarm bell circuits, the testing instruments, and the batteries for the whole system, are placed. An operator or watchman, the only one required for controlling the whole system, la also stationed here.
The instruments receiving the communications, either of fire or police, from the signal boxes, consist; first, of three receiving magnets mounted on the same stand, and connected, one with each of the three signal circuits; and, second, of a triple office alarm or call and a Morse register, with three electro-magnets, levers, and pen points, marking side by side on the same strip of paper, which alarm and register are operated by the receiving magnets and a local circuit. The office alarm consists of three powerful electro-magnets, each striking a blow by means of a hammer connected with the armature on a bell of a tone different from the others. A separate alarm and record is thus obtained for each signal circuit.
The signal of a fire having thus been received at the central station, the operator turns at once to the transmitting apparatus connected with the alarm bells, which consists of the district key-board. This instrument, in its simple form, is a circuit cylinder, carried by clockwork, with keys marked with the district numbers, which bear upon the cylinder when depressed, and complete the circuit at intervals, so as to produce the district signal on the bells with proper pauses, so long as the key is held down. The district key-board may also be constructed in a way similar to the striking motion of a common clock, so as to complete the circuit the requisite number of times when the key of each district is depressed by the action of a gathering pallet. This gives less numerous surfaces of electrical contact, and is therefore preferable, and has been adapted to the system at Boston by Mr. Farmer. It has seven keys for the fire districts, one key for continued blows at two seconds' interval, or fast ringing at the commencement of an alarm, and one key which gives the signal one, one-two for "all out," which is always to be struck upon the bells when a fire is extinguished, to allow the engines which have not reached the fire to return home. There are also two spare keys not yet appropriated.
For the sake of economy in battery power, the current is thrown on to the three alarm circuits, separately, but in rapid succession, by the arrangement of the key-board. The effect of this upon the synchronism of the bells is inappreciable, when compared with the effect of distance upon the sound of different bells.
An alarm-bell register is connected with the district key-board, having a dial for each alarm circuit. This is so constructed, by means of an electro-magnet armature and ratchets, that a hand on each dial is carried forward one-thousandth of a revolution each time that the battery current is sent out to the alarm bells. It Is consequently known in the office bow far the various striking machines have run down, and if it is necessary to wind them In anticipation of their usual weekly time.
The testing apparatus consists either of a common clock or an electro-magnetic clock, so arranged as to send the current of a testing battery over all the circuits once an hour, or more frequently. Each circuit communicates with an electro-magnet having an armature carrying a hammer, and striking a bell when the circuit is completed. At the City Building, in Boston, an electromagnetic clock thus test* the continuity of all the circuits by a chime of six bells of different note, at the regular striking time of the clock. The battery employed is purposely so feeble that it will not set off the striking machines in the alarm belfries.
The keys upon which the clock operates as above, are attached to a single board, and are also finger-keys, by which the circuits may be tested at any intermediate time. The three testing keys of the signal circuits have also the important function of police communication. By means of these, communication can be held backwards and forwards between the central station and the forty signal boxes. The signal battery connected with the closed signal circuits, at the central station, is about twelve Grove cups. The battery connected with the alarm circuits, and sufficing to liberate the hammers of all the hells is about thirty-fire Grove cups, though a smaller number may easily be used. This battery, in the south circuit of three and a half miles, liberates nine bell-hammers at the same instant.
There are nineteen alarm bells included in the three alarm circuits, which are called into action at will by means of the electric current. In the belfry of each of these is a powerful striking machine, which will now be described. This resembles the striking movement of clocks, made, however, to strike only one blow, and having, as its chief peculiarity, the very beautiful secondary electro-magnetic apparatus for the liberation of the detent, contrived in 1848, by Mr. M. O. Farmer, and for which, or its equivalent, in a weight or spring, he has applied for a patent in its application to machinery. The figure represents the precise form of instrument as well constructed by Howard and Davis for the city of Boston. For striking the large church bells they ire at present carried by weights of about twelve hundred pounds, and raise a hammer of 45 Lbs. on a handle four or five feet long. The hammers strike through an arc of from two to three feet, with a force equivalent to 800 Lbs. falling one inch.
The frame is a most substantial casting. The electro-magnet will readily be recognised, with its armature attached to an upright lever at c. The legs of the electromagnet consists of half-inch soft iron, surrounded with coils of insulated copper wire, No. 23, which are three inches long and two inches in diameter, a is a falling arm, weighted at the top, which is supported in an upright position by a horizontal lever, resting on the top of the armature lever at b. When the armature is attracted to the magnet, the weighted arm a falls over until stopped by the adjustable rest in front of it. In falling, a little lever, seen attached to the same axis, nines the latch-shaped detent d by means of the pin connected with it. The arm carrying the pin e, attached to the same axis with the cam y, and connected with the train of wheels of the striking machinery, is thus liberated, and commences to revolve on its axis. In so doing, the cam g swings forward the bar f, attached to the axis of the falling arm a, which is thus raised to its original position; the horizontal lever catches again at b if the armature has been released, the detent d falls, and the pin e is arrested at the end of one revolution. This occupies two seconds, and in the meantime the weight of perhaps 2,000 Lbs. has fallen an inch, and a single blow his been struck by the hammer. If the armature were not released from the attraction of the electromagnet, the horizontal lever would not catch at b, and the machine would continue to strike until the circuit influencing the electro-magnet was interrupted. This indefinite and undesirable mode of striking would be produced by holding down the alarm key at the central office. To obtain single blows, for the purpose of definite alarm, the circuit must be completed momentarily at suitable intervals, which is best effected by means of the district key-board. The fly-wheel of the clock-work is shown at h. The hammer represented in the figure is usually placed in a belfry above, connected with the hammer lever by a wire.
As part of the bells in the Boston system are also rung for other purposes, an automatic shut-off or switch is connected with the bell-frames, so that the battery current is diverted from the coils of the striking machine when the bell is In motion, and strikes a little electro-magnetic call to inform the sexton that there is an alarm of fire, to which he should give precedence by ceasing to ring.
An apparatus has been described by Messrs. Channing and Farmer for furnishing a constant supply of condensed air by means of the water under pressure in the pipes in cities, which may be applied either to carry a bell-hammer, by means of an air- engine, or, still better, to operate an air-whistle by means of the telegraphic circuit. The water metre of Huse, or other water engines may also be used to lift the bell-hammers. The advantage of such an application is the constancy of the power without the necessity of winding up and consequent limit of force and number of blows.
The experiments recently made in Boston show that the signals are instantly received at the central station from the most distant signal boxes, and that a reply is at once given on the bells with precision and certainty. The striking machinery is not yet adjusted so as to develop the whole amount of sound which can be obtained from the largest bells. As alarms are given by tolling hammers in New York and other cities, no difficulty will be found in bringing out any required amount of sound, in accordance with simple mechanical laws. The telegraphic and electro-motive part of the system, which is the novel part, is perfect and unerring in its action. It is worthy of notice that the circuits in Boston have not been interrupted by any casualty during this winter of unprecedented severity since they were first completed in December.
To show the operation of the system, let us now trace the alarm of fire which, in describing the signal box, we supposed proceeded from district No. 3, station 4. The operator at the central station, on receiving the signal, immediately passes over to the district key-board, and holds down the key for fast ringing. All the nineteen bells immediately begin to strike two second blows. After a minute or two the operator raises his finger, and then depresses the key marked 3. The bells now strike the district signals of three blows at intervals of two seconds, and then pause six or eight seconds and repeat, as long as the key is held down. Very soon a hurried signal is received over one of the signal circuits. This comes from the random rapping of an engineer on the key in one of the Signal-boxes, and is understood by the operator as an inquiry for the number of the station from which the alarm proceeded. This the operator immediately communicates by counting four raps by means of his testing key on the electromagnet in the signal box, from which the inquiry came. The engineer now knows the locality of the fire within fifty rods, and heads the engines directly to the spot.
Meanwhile the fire is perhaps easily extinguished. The engineer in command sends to the nearest signal-box, and taps one, one- two—one, one two, on the key. The operator at the centre receives the communication, and forthwith depresses the corresponding key of the key-board. The nineteen bells at once strike the signal a few times, and the engines in all parts of the city turn back.
By a multiplication of signal stations, and a suitable provision of bells, the telegraph alarm system becomes instantaneous, universal, and definite in its operation. The experience gained in the construction in Boston, will make the application in other cities and towns comparatively easy. In cities like New York, where there are a few large alarm bells, the telegraphic machinery can be applied with great advantage, BO as to strike a blow of any required force, and to bring the bells into operation separately or together, so as to limit or extend the alarm. Only one person is required at the centre to wield the whole of such a system, which provides also for a vital organization of the police body throughout the whole municipality.
The expense of the system, completed in Boston, maybe estimated at 15,000 dollars. For small towns a similar organisation might be effected for 1,500 or 2,000 dollars, and for the largest city, as New York, the work might be constructed in the most perfect and elaborate manner, bringing every building, as in Boston, within fifty rods of a signal-box, for about 50,000 dollars.
The government of the city of Boston deserve credit for the liberality with which they have thus brought a new application of science to the test of construction. Great credit is also due to Mr. Farmer, the superintendent of construction, in addition to his original contributions, for the practical direction by which the parts of so extensive a system have been brought into harmonious action.
The purpose of a Fire and Police Telegraph is to connect the various parts of a municipality by an intelligent and co-operative law. To accomplish this it has been found necessary to adopt for the municipal body the precise arrangement which is found in the nervous system of the individual.
Thus, in the fire telegraph now approaching its completion in Boston, there is a central station, which is the "brain," the common reservoir of nervous or electric force for the whole system, at which all the batteries are placed, and which is presided over by an intelligent will (the watchman or operator of the central station). From this centre radiate two classes of electric conductors or nerves (the iron wires carried over the houses). The first of these, the "signal circuit," conveys impressions to the centre, is "afferent," "sensitive," to adapt the language of anatomy. The second of these the "alarm circuit," conveys impulses from the centre, is "efferent," "motor." When any disturbance or alarm occurs at the circumference or other part of the system, it is signalized from the "signal boxes," which are scattered throughout the city, and which are the "sensitive extremities" of the sensitive conductors, to the central station, from which, after an act of intelligence and volition by the operator, an impulse to appropriate or corresponding action is sent over the "motor" nerves or conductors to the various belfries, where the electric or nervous agent animates iron limbs by means of the contraction of electro-magnetic muscles, thereby releasing powerful machinery to strike a single blow with each of the tolling hammers. By a combination of such blows, by the intelligent act of the presiding will at the central station, distinct signals, or any others, may easily be struck.
This presents at once an outline of the municipal fire telegraph. The analogy with the living system has been thus wittily stated by the editor of the Boston Commonwealth: "Suppose a live coal drops on your toe; the nerves of sensation give an instant signal to the brain,—that is, a feeling of pain. The brain then, by an act of will, conveyed to the muscles along the leg by the motor or alarm nerves, rouses the said muscles to their duty in the case, and the result is, that the coal is kicked off. The municipal fire-alarm arrangement is conducted on this very plan." The perfection of this analogy is a guarantee, in addition to the various ends of security and intelligent action which are thus obtained, that the arrangement is in conformity with a natural law.
A chief peculiarity of the fire telegraph, as a mechanical system, will be seen at once from the sketch above given. It developes the motor functions of the electric circuit, at a distance. Hitherto the telegraph has been chiefly used to convey intelligence, which is its sensitive function. Its application to the development and control of power at a distance, either by its own electro-magnetic energy, or by bringing into action other machinery, which is its muscular or motor function, is to give a wide extension hereafter to the uses of the agent—electricity. In the fire system, both of these vital functions of the telegraph, so to speak, are employed, and also related to each other in their natural order. In proportion as civilization advances, the telegraph is thus to constitute the nervous system of organized social life, relating all the parts and making possible a more perfect co-operation than could otherwise be obtained.
The municipal electric telegraph, applied to purposes of fire and police, was first described in its general principles by Dr. Wm. F. Channing, in 1845. In 1848 its adoption was recommended by Mr. Josiah Quincy, Jun., the Mayor of Boston, and some experiments were made. In 1851, an elaborate plan was finally presented by Dr. Channing to the government of that city, which was adopted, and is the basis of the system which has been constructed and successfully tested, though not as yet publicly introduced in Boston. The present mechanism and arrangement of the system have been elaborated by Dr. Channing and Mr. Moses G. Farmer, the able Superintendent of Construction.
We shall now proceed to describe the system in its various parts, and with its essential safeguards. The conditions by which permanent electric conductors may be established in a city, is the subject of first importance for all applications of the municipal telegraphs. This may be effected by the following means:—1st. By employing large wires (No. 8) of the best quality of Swedish iron. 2nd. By attaching them to the brickwork of buildings in the most substantial manner by means of wrought-iron brackets holding the insulators. 3rd. By selecting public buildings, or lofty isolated buildings, as points of attachment. 4th. By using as long stretches as is consistent with entire safety, say from 200 to 400 feet. 5th. By using duplicate wires, following different routes, between each and every station, (in exposed situations every triplicate wire may be employed), 6th. By avoiding the use of the ground as any part of the circuit. It is well known that the telegraph wires in our cities are very permanent. With proper guardianship, and means of testing a system of duplicate wires, constructed with the above precautions, cannot be interrupted under ordinary circumstances by chance or design.
The insulator used in the Boston system is Batchelder's patent, which is here represented.
The cast-iron cap is represented by the black line in the section. This is lined throughout with glass by the operation of blowing, or with porcelain. The shank is then introduced with a hot mass of glass, or any fused or semi-fused material, by which it is firmly fired in its place. This is represented by the shaded portion. Between the lower edge of the cap and shank, in the section, there are four inches of glass surface. The re-entering angle of the lower part of the cap protects the glass within from missiles, and is calculated, in a storm of wind and rain, to drive the latter downward, and thus preserve the insulation. The wires pars over the top of the insulator. The shank, which should be longer than is represented, screws into a bracket or the ridge-pole of a house.
Instead of wires insulated above the buildings, they may be buried in tubes under the streets of cities, though at a great increase of expense. In Boston the wires erected (about fifty miles in length) have cost less than 100 dollars per mile, though a plan of erection, which would cost 150 dollars per mile, is recommended by Mr. Farmer for future constructions. The mode of erecting wires, which has been described, applies to all the forms and uses of the municipal telegraph, amongst others to that of furnishing uniform time to a city.
At every station (sixty in number in Boston) dischargers for atmospheric electricity are provided, by presenting points, connected with the ground, in close proximity to the conducting wires.
The circuits of the fire system are divided as already stated, into those of "signal" and "alarm,"—the one conveying intelligence to the central station, the other conveying the impulse to mechanical action from the central stations to the hammers of the alarm bells. In the signal circuit the battery may be either constantly on or off, the signal being made in one case by breaking, in the other by completing the circuit. Unless the wires, are erected with very great care, the "closed circuit" arrangement is decidedly preferable. In this case, the duplicate wires, between each of the signal boxes on stations, diverge so as to resemble, in the whole circuit, the links of a chain. The signal here is made by breaking the circuit at any one of the signal boxes. Where the open circuit is used, the positive and negative wire is brought to each signal box, and the signal is made by a cross connection between them. The principle of duplicate conductors is preserved by letting each positive and negative wire form an entire circuit, and return to the pole of the battery from which it started. Each signal station is, therefore, connected with the battery at the central station, by wires following two different routes.
The alarm-bell circuit U arranged like the open signal circuit, and the power of the buttery is only thrown upon it when the brill are to be struck.
In large cities great economy and security is obtained by increasing the number of circuits of each kind. That, in Boston, there are three signal and three alarm circuits to different parts of the city, which come in separately to the central station, and which limy be kept and used entirely distinct.
In case of fire, the operation of the system begins at the signal box or station. Of these there are forty in Boston, distributed at distances of one hundred rods apart. They are so constructed that police communications may be had backwards and forwards between each of these stations, and the centre, in addition to their function of signalising an alarm of fire. By a similar coincidence, a fire and police telegraph baa been constructed in Berlin, Prussia, at the same time with that in Boston: this resembles simply the signal circuit and apparatus of the Boston system, but has not the novel and remarkable feature of the latter—the motor or alarm circuit, by which the bells are struck. In Berlin the public alarm continues to be given in the ancient mode, by blowing horns. It ia stated that in Berlin there are forty-six signal stations for the private communications of the police and fire department, connected with the centre.